Photo/IllutrationThe Asahi Shimbun

The green light has been given to freeze the remaining section of a “wall of ice” in the hope of blocking groundwater from entering the reactor buildings at the embattled Fukushima No. 1 nuclear power plant.

The Nuclear Regulation Authority gave the go-ahead Aug. 15 for the plant's operator, Tokyo Electric Power Co., to start the final freeze of a 7-meter section of the 1.5-kilometer long frozen underground soil wall on Aug. 22.

However, it is not known if the move will prove effective in cutting the volume of groundwater mixing with highly radioactive water at the plant, and it is expected to take months to completely freeze the final section.

The government spent 34.5 billion yen ($312 million) on the ice wall project, which began in March 2016 to help deal with about 400 tons of contaminated water being produced daily.

The project involves 1,568 pipes that were placed into the ground 30 meters deep around the four reactor buildings to circulate liquid at minus 30 degrees and thereby freeze the soil around them.

The underground ice wall is supposed to block the groundwater from flowing into the reactor buildings.

The NRA had held off its approval for the remaining section out of concerns that the contaminated water inside the buildings might overflow if the complete freeze caused TEPCO to lose control of the groundwater level.

But the watchdog finally gave the nod as the utility insisted that the groundwater level can be controlled by adjusting the volume of it pumped up through wells built inside the wall.

The daily amount of contaminated groundwater produced plunged from the 400 tons to about 140 tons after the ice wall was built.

TEPCO estimates that the number will drop to about 100 tons or less if the ice wall is completely frozen.

But the NRA believes the key reason behind a decline in polluted water is the work to pump up groundwater inside the wall, not the frozen barrier itself.

“Even if the underground ice wall freezes completely, its effect will be limited,” an NRA commissioner said.